U0484 High Generic / SAE

U0484: Invalid Data Received From Lighting Control Module — Rear A

Network and Communication Invalid Data Received

What to do

Before you drive anywhere, get somebody to stand behind the car while you work through the brake pedal, the indicators, the hazards, the lights, the fog light and reverse gear.

That is not a formality. Every light this fault affects is behind you, so you cannot see any of them. A headlight that fails is obvious the first time it is dark. Brake lights that have stopped working are invisible to you and remove the only warning the driver behind gets — which is why this one is worth a minute in a car park before anything else.

Then, if you tow: unplug the trailer or caravan and see whether the fault clears. On most cars the same computer runs the trailer socket and checks its bulbs, so a fault in the trailer, a wrong-wattage bulb, or a towing kit that was spliced into the wiring rather than fitted properly will produce this code with nothing wrong on the car at all. That test is free and it settles a lot of these.

Otherwise, mention any water in the boot — a damp spare wheel well, condensation inside a rear light — and any work involving the boot trim or a stereo installation.

If any brake light, indicator or rear light is not working, the car should not be driven until it is fixed, and in most places that is a legal requirement as well as a sensible one.

What this code means

The rear lighting control module is broadcasting data that cannot be accepted as true. See U0400 for the family's framing and U0483 for how modern lighting is driven.

This code carries a higher severity than the rest of the lighting family for one reason, and it is worth stating without decoration: the driver cannot see any of the lights this module operates.

Brake lights, indicators, tail lights, fog lights and reversing lights are all behind the driver. A headlight that fails announces itself on the first dark road. A brake light that fails announces itself to nobody at all — and a vehicle braking with no brake lights is the single most consequential lighting failure there is, because it removes the only warning the driver behind gets.

So the first action on this code is to have somebody stand behind the vehicle and go through every function. It takes a minute and it is the whole safety content of this page.

The rest is diagnosis, and there is one free test that resolves a large fraction of these. On most vehicles the rear lighting module also drives the trailer socket and performs the bulb-failure detection for it. A trailer or caravan plugged in with a fault, a bulb of the wrong wattage, or a towing loom spliced into the harness rather than fitted through the vehicle's proper interface, makes the rear module report currents that cannot be reconciled with the lamps it believes it has.

So: unplug the trailer, clear the code and see whether it returns. If it does not, the fault is in the trailer or its wiring rather than in the vehicle, and that is a far cheaper conversation.

After that, the causes are the rear of the car's usual list — water reaching the module through an aged tailgate seal or a hardened light cluster gasket, connectors behind the rear trim disturbed for boot liners and audio work, and the harness through the tailgate hinge, which flexes like a door boot and fails the same way.

And the same expensive note as U0483 applies. Rear clusters are increasingly sealed LED assemblies with no serviceable parts, so it is worth establishing whether the fault is the module, the wiring or the lamp before an assembly is ordered.

Likely causes

Start here

Poor wiring splice in an aftermarket installation · moderate
Water ingress into module · moderate
Corroded or loose connector · easy
Broken wire in the door harness boot · moderate

Less common

Damaged wiring harness · moderate
Damaged data bus wiring · moderate

Symptoms

Components involved

Information, not instruction

CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.

Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.

Community experience

Be the first to write this up

Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.

What makes one worth reading:

The car — make, model, year and engine. The same fault behaves differently on each.
What you measured, not only what you replaced.
What actually fixed it — or that nothing did, which is worth knowing too.